In an optical scanner, a polygon mirror having a regular polygon shape is fitting to a rotor shaft together with a rotor. Concretely, a rotor yoke is rotatably attached to the rotor shaft, which is rotatably held by a stator housing. The polygon mirror is attached to the rotor yoke in a state where the polygon mirror is prohibited from rotating with respect to and detaching from the rotor yoke. To avoid deformation and strain, the polygon mirror is attached together with the rotor yoke without being directly fixed to the rotor shaft. However, the polygon mirror is attached to an end part of the rotor shaft, so the polygon mirror is axially pressed toward the rotor yoke, so as not to detach, by a biasing member, e.g., plate spring, capable of biasing a top plate part of the rotor yoke (see Patent Document 1).